Proper Static Sag for CRF250X


13 replies to this topic
  • Codeman00

Posted January 03, 2010 - 03:43 PM

#1

Suspension Gurus, I have a question about rear spring rate vs static sag vs race sag...

I just bought new springs for my 2006 CRF250X and checked 3 calculators before I bought the springs. I had the stock spring in before I changed it out.

Weight 175 lb without gear
Riding is Enduro / Trails mostly / occasional MX track

Racetech (based on rider weight)
Stock Rear 4.8 kg/mm
Suggested Rear 5.12 kg/mm

GnarlyMX (based on rider weight)
Stock Rear 4.8 kg/mm
Suggested Rear 5.1 kg/mm

MX-Tech
Stock Rear 5.1 kg/mm
Suggested Rear 5.2 kg/mm

I went with a 5.1 kg/mm rear spring and just set my race sag to 101mm. My free sag was measured at 32mm. My manual and other resources say that the free sag should be 10-25mm and that anything over 25mm means that the spring is too stiff. Other resources say 20-40mm is the desired range. Which one is correct?

Should I be concerned with 32mm of free sag when the calculators tell me that 5.1 is the correct spring? Is this okay or do I have to buy another spring and change it out again? If I went to a 5.0, would it fix my free sag? Why would the calculators be off?

  • rks1

Posted January 03, 2010 - 07:49 PM

#2

At 175 w/o gear (approx. 200 with?), I don't think a 5.1kg is too stiff. I'd think you need at least a 5.3kg. Are you sure your measuring the sag correctly? Is someone helping you? In other words, you aren't trying to take the measurements on your own, right?

  • Codeman00

Posted January 03, 2010 - 08:16 PM

#3

I'm not sure how much I weigh in gear but I did have it all on. I have read a lot and I do have someone helping me take the measurements....

1) Baseline - First, I placed the bike on a stand with the wheel off the ground and measured from the axle to a point on the number plate (directly above the axle. In actuality, I set the Motion Pro Sag Scale to show zero at that point since its my baseline. My reading is 0mm.

1.5) Static Sag Check just to check where my static sag was before the race sag was set, I measured it to be 60+mm....I don't remember it exactly, but I figured I was in trouble at that point.)

2) Race Sag - Next, I took the bike off of the stand stood directly on the footpegs with full gear and measured the race sag...it was off the scale (too high). I cranked on the nut little by little and set the race sag to 101mm with a friend reading the measurement off of the scale. I had to get on the bike several times and make several adjustments before I got it to exactly 101mm. I verified the measurement every time buy bouncing on the bike and getting at least 2 measurements.

3) Static Sag - I then got off the bike and measured the number plate mark with the bike on the ground with no rider....the reading was 32mm. (I bounced it several times to and took another measurement to check it).

I'm pretty sure I'm doing it right...can you verify that? So you think that my results are fishy? I thought so too....which I guess is why I'm here.

  • mog

Posted January 04, 2010 - 07:16 AM

#4

32mm free sag is fine.

  • highmarker

Posted January 04, 2010 - 08:21 AM

#5

when doing your free sag, push down on the seat and let it return, measure. Than lift up on the seat and let it settle, measure. If it's different average the two.

also if working with a new spring it may change after a few rides

the 1", 4" thing is just a ballpark, you may want to adjust some either way to get the bike to turn the way you like. a 1/4 " either way isn't going to change the suspension action

  • Codeman00

Posted January 04, 2010 - 11:06 AM

#6

I will try the opposite way of measuring the static sag. Can you explain why this method should be used instead of the method that I did? Do some suspensions not bounce back to the full position?

  • Codeman00

Posted January 04, 2010 - 09:05 PM

#7

Highmarker,

If I compress the spring and let it up gently, I get 42mm. If I pull the spring up and let it slowly settle down, I get 32mm. I guess, I'm even worse then...about 37mm average. I don't have any of the compression clickers moved at all from the time that I removed the springs...I'm not sure if that makes any difference though since we're worried about the spring. I really want to understand what's going on and why the calculator is off. Is there anything from the above test method that I might be doing wrong?

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  • 07400E

Posted January 04, 2010 - 09:24 PM

#8

Codeman,

I'm 84kgs, no gear,and get similar specs to you with my stock rear spring - all measured properly with a helper.

What have you noticed when riding the bike with the stiffer rear compared to stock ?

  • Codeman00

Posted January 05, 2010 - 11:05 AM

#9

Unfortunately, I haven't had a chance to ride it yet due to a broken finger that has finally healed and now a cold snap in the bitter teens. It might be awhile until I get to do something other than ride around the block for a test ride.

I looked back at my old readings and I was at 100 race and 30 static sag with the stock spring...same as this spring??..although that spring was for 160 lb rider which I am not. (I can't verify those measurements because I might have done something wrong back then). In hindsight, I should have measured it again before I removed the stock spring. I don't know how the stock spring can be too stiff? None of this makes sense to me right now. Hopefully someone out there can help.

  • highmarker

Posted January 05, 2010 - 05:23 PM

#10

Those online calculators are helpful in getting you in the ballpark but there is no really perfect spring. Some of the shops tend to use lighter springs and slow the dampening. or heavier springs and speed the dampening depending on the rider terrain etc. The x's linkage ratio is different than the R, so do the calculators take that in consideration? or do they just go by book bike weight? and do they presume a X rider might ride a slower pace? and so on. At your weight I think your fine with what you got, it is honda's option for heavier than standard. If you go much heavier you'll want to change the fork springs too because you'll be riding higher in the stroke and the front won't.

  • Codeman00

Posted January 05, 2010 - 09:25 PM

#11

Understood, highmarker. I probably do have at least "closer to the correct" spring for my weight which is what I wanted. Everyone says that the stock spring is a 4.8 and its made for a 160 lb rider...the calculators all show a 5.1 or a 5.2 for my weight. Everyone says that I need a stiffer spring. Unfortunately, the sag numbers are confusing everything. Even more confusing is that my sag numbers say I need to go softer, the MX-Tech calculator says I am perfect, and the MX-Tech mod says that I need to go more stiff! Someone has to be right...? And if my race and static sag measurements with the 4.8 showed that I needed a softer spring, then something is definitely wrong! ...:cheers:

I think I'm just going to stick with the 5.1 and see how it goes....its too bad I can't understand this a little better....but I will keep on reading. I'm an engineer and it drives me nuts not to understand this. Thanks for the help.

By the way, my front springs were changed out with the rear spring...from 0.42 to 0.44 kg/mm....so its all balanced out :moon:

  • mog

Posted January 06, 2010 - 03:51 AM

#12

you need to recheck your sag numbers, and if they are within range then dont worry.

  • highmarker

Posted January 06, 2010 - 06:00 PM

#13

There is another factor in sag measurement that is seldom mentioned (since your an engineer, LOL). The dimension with the bike on the stand, wheel elevated, is usually greater than the same test done by merely lifting the back of the bike to eliminate play in the suspension. On the stand the weight of the swingarm will compress the top out built into the shock. Just lifting on the back of the bike won't do this.

Only reason i mentioned it is it can effect your starting measurement.

One thing you might notice right off with the change to .44's in front is the fork will ride a bit higher slowing the steering. Stock I felt the bike to steer very neutral, when "I" did springs (.45 and 5.3), right off I noticed it steered slow, so I left the sag and slid the forks up a bit. Something to think about anyway.

FWIW, I'm 190 and thought the stock susp and clicker setup worked pretty good for a reasonable pace in the woods. With some groups I ride with i would have just left it. But I pretty much do everything from enduro to harescramble pace with this bike so I went ahead and sprung it for such. I think the valving is great and haven't touched it, just oil changes.

  • Codeman00

Posted January 06, 2010 - 06:18 PM

#14

(Being an engineer says a lot I guess!:moon:)

Interesting stuff about the top out of the shock. I'll have to check it out this weekend when I check through everything one last time. It would be interesting to see how much of a difference that makes.

In addition to the 0.44's, I did already move the forks up about 2.5mm in the triple clamp...so maybe I won't notice as much in regards to turning issues. Crazy though that the fork springs would make that much difference in turning. This is going to be interesting to ride again and see the difference.

I've read too that the stock X valving is pretty good...I doubt if I'll ever touch that either.

One more question...what sag do you run? Everyone seems to have a different opinion on this. I was thinking about going down to 98 or so...just curious what you recommend. I've pulled the clicker settings off a few websites...so I think I'm good to go there.





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